1. Field of the invention
The present invention relates to a light-emitting diode (LED) array and, more particularly, to a method for making a LED array capable of realizing a large output and a large-scale integration by using a heterogenous film which can electrically insulate between LEDs by the diffusion of an impurity into a substrate.
2. Description of the Prior Art
At a high information-oriented age, as the data processing capacity of automatic devices such as computers increase continuously, a printer as a data outputing device also requires high-speed, high-resolution and multi-functions. As a result, to meet such a requirement, a LED array in a LED printer utilizing an electrophotographic technique is asked for large output and large-scale integration.
FIG. 1 is a schematic diagram showing a portion of a known LED array. There is explained a preferred embodiment by the prior art. Over an N-type GaAs substrate I is entirely formed an N-type GaAsP film 2 and selectively formed an insulating film 3 given portions, there is formed a zinc diffusion region 4 over the parts of the N-type GaAsP film 2 on which the insulating film 3 is not formed. Also, a P-type electrode 5 from a side of the zinc diffusion region 4 to the upper insulating film 3 and a N-type common electrode 6 under the N-type GaAsP substrate are formed. The region, wherein the insulating film 3 is not formed, is utilized as a luminescent region 7. There is formed a P-N junction between the N-type GaAsP film 2 and the P-type zinc diffusion region 4 formed by the diffusion of zinc into the N-type GaAsP film 2. Therefore, when a voltage is now applied between the N-type common electrode 6 and the P-type electrode 5, a light emission is radiated from the luminescent region 7.
However, the P-N junction formed by the same material as above mentioned becomes Homojunction, so that it has a problem that a high-speed printing is difficult due to a small luminescent output at the junction interfaces. Moreover in another preferred embodiment of the prior art, if Mesa etching is performed for separating between elements after growing heterogeneous film for increasing a luminescent output, it has a difficult problem in that the forming electrode and a large-scale integration cannot be successfully achieved because the surface of chip isn't flatten.